"PhD Studentship: Exploring Saturn’s polar hexagon using numerical models, Mathematics PhD (STFC funded)"

University of Exeter - ESE

One of the solar system’s most eye-catching features is Saturn’s famous ‘polar hexagon’. There has been much interest from both the public and scientists as to how such a hexagonal structure could arise, and how it could be sustained. Current theories think of the hexagon as a standing Rossby wave sitting on top of a jet stream, with such a wave possibly arising from an instability of the jet. Laboratory studies of Saturn’s hexagon suggest that barotropic shear instabilities can give rise to hexagons and other shapes. This would imply that the hexagon is sustained by extracting energy from the underlying jet stream. However, recent observational studies have indicated that the hexagon is doing the opposite, i.e. it is giving energy to the jet, rather than extracting energy from it (Read et al 2022). There are several possible solutions to this energy transfer conundrum. One is that the energy transfer is periodic – sometimes the hexagon feeds off the jet, and sometimes it gives energy back to the jet. Another is that the hexagon is a baroclinic wave of the type found in both lab and model studies (see Wang et al 2018 and references within). In this project we will investigate both of these possibilities using a combination of numerical simulations of the shallow water equations (building on the work of Rostami and Zeitlin), as well as state-of-the-art global simulations of Saturn with the Isca climate modelling framework, developed by the supervisory team and others here at Exeter.

As the project progresses, we will widen our focus to study the polar regions of giant planets in general, looking at how planets including Jupiter and Saturn transition from strong jet streams in their lower latitudes through to polar turbulence and polar vortices in their highest latitudes (building on earlier work by Theiss). The exact direction of the project will be flexible, allowing the student to follow their own interests within the area of giant-planet fluid dynamics.

The project will give the student a deep understanding of atmospheric fluid dynamics on giant planets and how their atmospheres compare with Earth. The student will be embedded within an active and growing research group on atmospheric dynamics across Earth and other planets, and will be encouraged to pursue collaborations within this group and internationally. The project itself will include funding for the student to attend international meetings and conferences, and will allow the student to develop excellent technical skills in the analysis and interpretation of atmospheric data and high-performance computing.